The present invention relates generally to systems, apparatus, and methods for the production of energy products from carbonizable material, such as biomass, particularly systems, apparatus, and methods that employ fast pyrolytic reactions.
Today, the United States faces substantial environmental issues from continuing reliance on polluting energy sources such as coal, natural gas, nuclear power, and hydroelectric power. The burning of fossil fuels, such as coal and natural gas, results in the emission of excessive amounts of carbon dioxide into the atmosphere. The use of nuclear power raises the specter of ecological damage through the accidental release of radiation into the environment, as well as difficulties in safely disposing of spent nuclear fuel. Hydroelectric projects can disrupt local ecosystems, resulting in major reductions in fish populations, negative impacts on native and migratory birds, and damage to the dammed river itself. As a result, people are looking for alternatives to these ecologically-harmful sources of energy. In recent years, biomass has gained popularity as an environmentally-sound alternative.
Biomass is commonly defined as living or recently-dead biological matter, generally vegetable matter. Biomass, or the fuel products derived from it, can be burned to produce power. Unlike fossil fuels, however, carbon dioxide released from the burning of biomass does not contribute to the overall carbon dioxide content of the atmosphere. This is true because biomass is part of the world's current atmospheric carbon cycle. For this reason, biomass is viewed as a renewable, carbon-neutral fuel.
Substantial sources of biomass are available from forest products processing facilities. The typical facility uses some of its biomass in the creation of its products, while the remainder of the biomass is seen as a byproduct. One type of forest products processor that produces a large volume of biomass byproduct is a chip mill. The chip mill processes only small-sized timber. In the chip mill, logs are debarked and then ground into chips for transporting to other mills for further processing. Another type of forest products processor is a chip and saw facility (“CNS facility”). A CNS facility produces dimensional lumber from timber that has a diameter ranging from mid-sized to small. Substantial sources of biomass are also available from other facilities, such as large log processing plants, plywood plants, and OSB plants, among others.
Throughout the year, a typical CNS facility will generate an average of more than five-hundred tons of dry biomass byproducts per day. (According to Marks Mechanical Engineering Handbook, the standard for “dry” is defined as twelve percent moisture content.) These biomass byproducts consist of white chips, bark, sawdust, and wood shavings. The white chips produced by a CNS facility are generally sold to paper-producing mills for processing into paper and cellulose products. The bark, sawdust, and shavings are either used at the CNS facility itself as a thermal energy source or sold as a byproduct. When sold as a byproduct, the biomass generally fetches less than twenty dollars a ton. This is far less than the value of its energy content, as shown by Table 1 below.
TABLE 1Typical Production and Pricing of Biomass from a CNS facilityWaterDailyValueEnergyEnergy ValByproductContentProductionPer TonPer PoundPer Ton *Bark10%300 tons$9.916,500 Btu$224.91White Chips40%700 tons$19.135,000 Btu$173.00Sawdust40%120 tons$13.005,000 Btu$173.00Shavings10%120 tons$24.508,666 Btu$299.86* The dollar value of the energy contained within a ton of a given type of biomass is based on a sale price of $100 for a 42-gallon barrel of crude oil having an energy content of 5,780,000 Btu.
One process used to produce energy products from biomass, and thus capture its energy content, is a process known as fast pyrolysis. Fast pyrolysis utilizes temperatures of between four-hundred-fifty and six-hundred degrees Celsius to rapidly heat biomass in the absence of oxygen. This results in the creation of three products: bio-oil, char, and non-condensing gases. All three products are combustible. The energy content of each of these products is listed in Table 2 below, along with the approximate percentage of each product typically yielded by the process.
TABLE 2Energy Content of Products Produced by Fast Pyrolysis% of ProductProductEnergy ContentYieldedBio-oil8,000 Btu per pound70.0%Char12,000 Btu per pound 14.3%Non-condensing Gases4,000 Btu per pound13.4%
Fuel needed to create and maintain such high temperatures in systems utilizing fast pyrolysis can represent a major operational expense. For this reason, it is recognized as desirable in the art to create systems that make the most of the heat they produce. There are a number of strategies used to accomplish this.
One strategy employs techniques meant to optimize the transfer of thermal energy to individual particles of biomass within a pyrolysis chamber. This can be accomplished through the use of organic heat carriers, like hot char, and inorganic heat carriers, like sand. These particularized heat carriers circulate within the pyrolysis chamber and radiate their heat to the particles of biomass. Other techniques involve rapidly moving particles of feedstock within a pyrolysis chamber so as to force the particles into nearly continual contact with the hot walls of the chamber. Still other techniques circulate a heated gas stream through a pyrolysis chamber to transfer heat to the particles of biomass. Another strategy involves capturing the hot exhaust resulting from pyrolytic reactions in the pyrolysis chamber and recirculating that hot exhaust to other parts of the system. Yet another more basic strategy involves simply insulating the pyrolysis chamber to deter heat loss through the walls of the chamber.
Given the desirability to make efficient use of the heat produced by systems employing fast pyrolysis to convert biomass into energy products, what is needed is a fast pyrolysis system that improves upon the conservation and reuse of a system's existing heat in a manner that is compatible with other recognized techniques for conserving and reusing the heat generated by the system.